Against the Fall of Night: Arthur C Clarke

This was a short Sci-Fi novel about a post apocalyptic Earth where only species of humans survived. Those who live life spans like ours (living in LYS) and those who have mastered how to live centuries(living in Diaspar). A child, Alvin, is born in Diaspar who is uncommonly curious. He questions if there are others on Earth and escapes his city to find them. He finds a community that believes as his does that outside influence will lead to disaster, but has a desire to make the two communities meet. The two communities are further characterized as Lys being rural where the people are telepathic and Diaspar being very technologically advanced where computers do all the tasks, but people live forever. Alvin finds a space ship and ventures out to another planet where no life exists. He feels something probe into his mind and takes it back to Lys. This presence has all the memories of the past, but is childlike and not described very well. In the end, through Alvin's restlessness and the presence of this supreme being, the people of Earth realize they can live together harmoniously and need each other.